The Whisky Production Process: Part 3 - Fermentation

September 03, 2017

The whisky production process is made up of 5 distinct steps and they are as follows:

- Malting

- Mashing

- Fermentation

- Distillation

- Maturation

The next stage in the whisky production process takes the product of the mashing process, or wort, and transforms it into an alcoholic substance with a similar consistency to beer known as wash. This process is known as Fermentation.

The fermentation process explained

The fermentation process begins when the wort which has been transferred to the underback is pumped into giant wooden or stainless steel receptacles known as washbacks and distillers yeast is added to the mix. The wort in the meantime has been cooled due to the presence of the heat exchangers which reside between the mash tun and underback.

The wort begins interacting with the yeast at between 20-25 degrees Celsius and the result is what is called a "weak beer" known as wash which is between 6-9% in abv. The yeast then either dies or goes inactive at around 34 degrees Celsius, thus signalling the end of the fermentation process.

Different distilleries utilise different fermentation regimes in order to produce the desired kind of wash character that is requires for their whiskies and this also means that the fermentation times can vary from as short as 48 hours to as long as 160 hours.

Shorter fermentation times tend to create wash which has a nutty and spicy character whereas longer fermentation times tend to create wash which has a floral, delicate and fruity character. Most distilleries, however, tend to adhere to an average fermentation time of about 72 hours.

The washbacks at Bowmore

At the end of the fermentation process, the yeast rises to the top of the wash when it is spent and this type of yeast is known as top flocculating in nature.

The most common strain of yeast used by distilleries these days would be the M Mauri varietal and this strain is a hybrid of both brewers and distillers yeast which has been engineered in order to efficiently produce the most amount of alcohol in as short a period of time.

In previous years and decades, distilleries were known for experimenting with different strains of yeast and it was not uncommon to see brewers yeast being used in the whisky production process. These yeasts yielded more fruity whiskies with a tropical note and one of the more well-known strains would be Stoke Newton which was used extensively by Bowmore and Laphroaig in the 1960-1980s period.

It is also known that the whiskies produced by both distilleries during this period exhibited a rather prominent fruity and tropical note and these whiskies are highly prized for their quality as well as rarity these days.

At the end of the fermentation process, the washbacks will be cleaned with a mixture of high pressure steam and caustic chemicals in order to ensure that there is no bacterial growth that can affect the next batch of wort being fermented within. Wooden washbacks are more susceptible to bacterial growth and they are therefore cleaned carefully and thoroughly. While stainless steel washbacks are less susceptible to bacterial growth, they are subjected to the same intense and rigorous cleaning process.

The fermentation process is the intermediate step in the whisky production process and aids in the production of alcohol which is crucial in the whisky production process. However, the alcohol produced is of a relatively low strength and so the wash will then be transferred to the wash and spirit stills in order to increase the alcohol strength to a suitable level. This process will be more thoroughly explained in the next stage: ﻿Distillation﻿.